Method for metering fuel to an internal combustion engine in conjunction with a hot start

Abstract

The invention is directed to a method for metering fuel for an internal combustion engine having a lambda control. In the method, characteristic parameters of the lambda control are changed in conjunction with a hot start of the engine. A leaning of the fuel mixture can be countered in a targeted manner by utilizing the lambda control to enrich the mixture. The bandwidth of the vaporizing performance of possible fuel types must not be covered by an averaged enrichment factor. For this reason, and for intense leaning of the fuel mixture, far greater enrichment factors are possible. The advantages afforded are that the additional measures such as raising the idle rpm are only initiated when actual hot idle problems are present. This is a further advantage in conjunction with the method of the invention. The measures of raising the idle speed can be used much more than previously since these problems occur infrequently and are clearly selectable with the aid of the method of the invention.

What is claimed is: 
     
       1. A method for metering fuel to an internal combustion engine equipped with a lambda control path which includes a lambda probe supplying an output signal, the method comprising the steps of: forming a base value for metering fuel to the engine in dependence upon operating parameters thereof;   superposing an actuating variable on said base value, at least intermittently, said actuating variable being based on said signal of said lambda probe and said lambda control path;   initiating measures to compensate a disturbance of the fuel mixture when specific conditions characterizing a hot start are present when the engine is started;   forming a quantity based on said actuating variable and comparing said quantity to a predetermined threshold value; and,   initiating at least one measure to increase the torque of the engine when said quantity exceeds said predetermined threshold value.   
     
     
       2. The method of claim 1, further comprising the steps of: measuring the temperature (Tmot) of the engine and the temperature (Ta) of the intake air; and, characterizing a start of the engine as a hot start when, in conjunction with the start, at least one of said temperatures (Tmot or Ta) exceeds a predetermined threshold value. 
     
     
       3. The method of claim 1, as an additional measure, further comprising the step of increasing at least one of the following variables of said lambda control: control range, integral component, proportional component or differential component. 
     
     
       4. The method of claim 1, further comprising the step initiating at least one of the following measures to increase said torque when said threshold value is exceeded: increasing the idle rpm; switching off possible loads such as the drive for climate control equipment; and, switching off other disturbing variables such as exhaust gas return and tank venting. 
     
     
       5. The method of claim 1, further comprising, after a hot start with a lambda probe which is not operationally ready, initiating measures for an accelerated activation of the lambda control. 
     
     
       6. The method of claim 5, further comprising initiating at least one of the following measures: increasing the idle rpm; retarding the ignition to later time points; and, advancing the time point of the start of the lambda control. 
     
     
       7. The method of claim 1, further comprising the step of carrying out a controlled enrichment of the fuel mixture. 
     
     
       8. The method of claim 2, wherein the threshold value for the temperature (Ta) of the intake air is determined by a pregiven offset Δt with respect to the measured value of the temperature of the intake air for the previous switch off of the engine.